Technical Field
The present disclosure relates to a semiconductor device with a buried conductive region, in particular a buried metallic region, and to a method for manufacturing the semiconductor device.
Description of the Related Art
In the field of semiconductor devices, deep doped layers (also known as “deep buried layers”) provided in the semiconductor substrate are frequently used. For instance, in bipolar transistors, vertical-diffusion DMOS (VDMOS) transistors, and trench-MOS transistors, heavily doped deep buried layers are used for improving the properties of the system. The deep buried layer provides in fact a low-resistance contact that extends underneath the device. In this way, for example, it is possible to reduce the resistance of the collector, in the case of a bipolar transistor, or the drain resistance in the case of a DMOS or VDMOS transistor for guarantying high speeds of response and low power consumption. The electrical contact with the deep buried layers is generally obtained by providing the so-called “sinkers”. A sinker is obtained by implantation of high-energy ions in the surface of the substrate and subsequent diffusion, for example by annealing at high temperature, of said ions in the substrate for a time sufficient for them to reach the deep buried layer that is to be contacted electrically. Other methods for producing electrical contacts with deep buried layers include etching the semiconductor substrate until the deep buried layers are reached and depositing metallic material within the trenches thus formed.
There is felt in the state of the art the need to replace the deep buried layers with metallic layers, which afford a wide range of advantages. A metallic layer is certainly more conductive than any implanted layer, even one having a high concentration of dopant species, and could thus replace the buried doped collector in bipolar transistors, with a reduction of the collector resistance. Likewise, in the case of VDMOS transistors the buried conductive region provides a highly conductive drain region.
Applications of devices including a buried metallic layer are multiple, and include optoelectronics, millimetric-wave components and circuits, and above all, integrated circuits for applications of a smart-power type, in particular for the automotive industry, in the industrial sectors in general, and in the industrial compartment of consumer goods.
Known techniques for providing buried metallic layers envisage coupling, via bonding, of previously machined semiconductor substrates. In particular, one of these substrates has a layer of metal (or a precursor of a metal) deposited by sputtering on a surface of the substrate, and the bonding base has the function of “burying” said layer. See, for example the scientific publication by W. L. Goh, et al., “Electrical Characterization of Dielectrically Isolated Silicon Substrates Containing Buried Metal Layers”, IEEE Electron Device Letters, vol. 18, No. 5, May 1997.
The known art presents, however, the disadvantage of requiring a step of coupling via bonding that proves costly, does not enable development of monolithic devices, and in general sets limitations on the metallic materials that may be used for the buried layer.